WO-A-95/26499 discloses a sensor based on a volume hologram. This sensor comprises an analyte-sensitive matrix having an optical transducing structure disposed throughout its volume. Typically, such a sensor is made of silver halide particles disformed in gelatin. Because of this physical structure, the optical signal generated by the sensor is very sensitive to volume changes or structural rearrangements taking place in the matrix, as a result of interaction or reaction with the analyte.
An alternative method of production of a holographic sensor is disclosed in WO-A-99/63408. A sequential treatment technique is used, wherein the polymer film is made first and sensitive silver halide particles are added subsequently. These particles are introduced by diffusing soluble salts into the polymer matrix where they react to form an insoluble light-sensitive precipitate. The holographic image is then recorded.